The present invention relates to an excitation coil for a fuel injector electromagnetic metering and atomizing valve on an internal combustion engine.
Known valves of the aforementioned type usually comprise a casing; a plunger moving axially inside the casing between a first position, wherein it opens a fuel injection hole formed in the front end of the casing, and a second position wherein said injection hole is closed; a core of magnetic material housed inside the casing; an anchor integral with the plunger; and an annular excitation coil designed to produce a magnetic field in the core for attracting the anchor and so moving the plunger into said first position.
Said coil substantially comprises an annular winding of electric wire, the ends of which are secured to respective pins connected electrically via various types of electrical connecting members. According to the embodiment described in patent application Ser. No. 67495-A/87 filed by the present Applicant and entitled "Fuel injector metering and atomizing valve on an internal combustion engine", the top end of each pin is connected electrically to a conducting bar substantially perpendicular to the pin. Said valve also comprises a plastic cap on the top, into which the ends of the pins and conducting bars are embedded.
On coils of the aforementioned type, the ends of the winding wire are connected to the respective pins by winding and welding the end portions of the wire on to the bottom ends of the pins. The resulting winding and pin assembly is then placed inside a mold into which thermoplastic material is injected for forming a casing about the winding and at the same time locking the bottom ends of the pins in relation to the casing.
Excitation coils of the aforementioned type present numerous drawbacks.
Firstly, electrical connection between the ends of the winding wire and respective pins is often unreliable, owing to poor contact and welding between the wire and the surface of the pin. Moreover, the connecting portion so formed between the wire and the ends of the pins is subjected to severe pressure, and may easily be damaged, when the coil casing material is injected about the winding and pins inside the mold.
Coils of the aforementioned type also involve a highly intricate, and therefore high-cost, manufacturing process, owing to the limited amount of access for welding between the winding and wire-pin welding area, and the care required for preventing damage to the winding by overheating.